Uncontrollable shivering!

I woked up after 1 hour or so after going to bed. Shivering uncontrollably, with teeth chatering. I'm not more cold than usualy! My heart was racing and my blood pressure was 136/70 while lying down. The shivering stopped about 30 minutes after I was up.

I am wondering if uncontrolable shivering / shaking can be related to Chiari. Did this happend to anyone else?

Postural orthostatic tachycardia syndrome (POTS, also postural tachycardia syndrome) is a condition of dysautonomia,[1] to be more specific orthostatic intolerance, in which a change from the supine position to an upright position causes an abnormally large increase in heart rate, called tachycardia. Several studies show a decrease in cerebral blood flow with systolic and diastolic cerebral blood flow (CBF) velocity decreased 44% and 60%, respectively.[2] Patients with POTS have problems maintaining homeostasis when changing position, i.e. moving from one chair to another or reaching above their heads. Many patients also experience symptoms when stationary or even while lying down.
Symptoms present in various degrees of severity depending on the patient.

This tachycardic response is sometimes accompanied by a decrease in blood pressure and a wide variety of symptoms associated with hypotension. Low blood pressure of any kind may promote the following:[3]
lightheadedness, sometimes called pre-syncope (pre-fainting) dizziness (but not vertigo, which is also called dizziness)[4]
exercise intolerance
extreme fatigue
syncope (fainting)
Excessive thirst (polydipsia)
Chronic or acute hypoperfusion of tissues and organs in the upper parts of the body are thought to cause the following symptoms:
cold extremities
chest pain and discomfort
disorientation
tinnitus
dyspnea
headache
muscle weakness
tremulousness**** this may be the shivering u had*****
visual disturbances
Autonomic dysfunction is thought to cause additional gastrointestinal symptoms:
abdominal pain or discomfort
bloating[5]
constipation
diarrhea
nausea
vomiting

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